(STATEHOUSE) - Opponents of a constitutional ban on gay marriage are warning the amendment's ripple effect could jeopardize health benefits offered by employers.

A gay marriage ban has been part of state law for 25 years, and supporters point out it hasn't affected domestic-partner benefits.

But this year's version of a constitutional ban adds language to ban civil unions too, outlawing anything "substantially similar".

Law Professor Deborah Widiss warns that "quite likely" could have unintended consequences, preventing companies and her own employer, Indiana University, from offering domestic-partner benefits.

Widiss says the authors of Michigan's Constitutional Amendment made similar assurances that benefits would not be affected, only to have courts disagree.

Indiana-based Cummins and Eli Lilly, who have publicly fought the amendment since it was first offered in 2005, and say their legal departments are still studying the effect on their benefits packages.

Managers for both companies repeated what's been the crux of their opposition at a senate committee hearing on Wednesday, arguing the amendment would make it harder to recruit top talent, and make them less likely to add jobs in Indiana.